From University of California, San Francisco, San Francisco, California; and University of Michigan, Ann Arbor, Michigan.

Acknowledgment: The authors thank Dr. David Glidden of the University of California, San Francisco, General Clinical Research Center for assistance with the Monte Carlo simulation.

Grant Support: By grants from the National Institutes of Health to the University of Michigan and the University of California, San Francisco, General Clinical Research Centers (M01-RR00042 and M01-RR00079), including a Clinical Associate Physician Award to Dr. Ladabaum.

Aspirin therapy in patients screened with sigmoidoscopy every 5 years and fecal occult blood testing every year (FS/FOBT) or colonoscopy every 10 years (COLO).

Outcome Measures:

Discounted cost per life-year gained.

Results of Base-Case Analysis:

When a 30% reduction in colorectal cancer risk was assumed, aspirin increased costs and decreased life-years because of related complications as an adjunct to FS/FOBT and cost $149 161 per life-year gained as an adjunct to COLO. In patients already taking aspirin, screening with FS/FOBT or COLO cost less than $31 000 per life-year gained.

Results of Sensitivity Analysis:

Cost-effectiveness estimates depended highly on the magnitude of colorectal cancer risk reduction with aspirin, aspirin-related complication rates, and the screening adherence rate in the population. However, when the model's inputs were varied over wide ranges, aspirin chemoprophylaxis remained generally non–cost-effective for patients who adhere to screening.

Conclusions:

In patients undergoing colorectal cancer screening, aspirin use should not be based on potential chemoprevention. Aspirin chemoprophylaxis alone cannot be considered a substitute for colorectal cancer screening. Public policy should focus on improving screening adherence, even in patients who are already taking aspirin.